Present day wireless communication systems, such as WCDMA (Wideband Code Division Multiple Access) continue to evolve to support high bit rate applications. As data rates increase, so does interference and self-interference from the dispersive radio channels, which in turn severely limits performance. In order to combat these problems, advanced receivers for WCDMA terminal platforms and base stations are continually being developed and further improved. Consequently, in future versions of mobile communication systems like WCDMA, Interference Suppression (IS) will be used in order to achieve better performance in terms of e.g. peak data rates, coverage, system throughput and system capacity.
Future cellular networks can also be expected to become more and more heterogeneous in terms of wireless devices, deployed radio network nodes, traffic demand and service types, and radio access technologies.
The interest in deploying low-power nodes (such as pico base stations, home eNodeBs, relays, and remote radio heads) for enhancing the macro network performance in terms of the network coverage, capacity and service experience of individual users has been constantly increasing over the last few years, although radio network nodes of different power classes have existed for a longer time. With the increased interest in such deployments, it has also been realized that there is a need for enhanced interference management techniques. This is useful to address the arising interference issues caused, for example, by a significant transmit power variation among different cells and cell association techniques developed earlier for more uniform networks. This problem has not been that crucial earlier since lower-power nodes have been used mostly in indoor environments for coverage enhancement of cellular networks and therefore there has been a good isolation from the interference caused by macro-layer transmissions. Nowadays, such nodes are also considered for outdoor deployments and for capacity enhancement in general.
In 3GPP (Third Generation Partnership Project), heterogeneous network (HETNET) deployments have been defined as deployments where low-power nodes of different transmit powers are placed throughout a macro-cell layout, to cope with a non-uniform traffic distribution. Examples of such nodes are pico-, micro-, and femto-base stations as well as relay nodes, or any mix of them. Such deployments are, for example, effective for capacity extension in certain areas, so-called traffic hotspots, i.e. small geographical areas with higher user density and/or higher traffic intensity where installation of pico-nodes can be considered to enhance performance. Heterogeneous deployments may also be viewed as a way of densifying networks to adopt for the traffic needs and the environment. However, heterogeneous deployments also bring challenges for which the network has to be prepared to ensure efficient network operation and superior user experience. This is because the mix of these different nodes introduces interaction between the cells in new ways, in particular, in reuse-one networks where the inter cell isolation is poor. The air interface load interaction becomes particularly difficult in heterogeneous networks of WCDMA type, equipped with so-called IS receivers.
To illustrate what may happen, consider a low power cell with limited coverage intended to serve a hotspot. In order to get a sufficient coverage of the hotspot an interference suppressing receiver is used. The problem is now that the low power cell is located in the interior of and at the boundary of a specific macro cell. Further, surrounding macro cells also interfere with the low power cell rendering a high level of neighbor cell interference in the low power cell, that despite the advanced receiver reduces the coverage to levels that do not allow a coverage of the hotspot, even if the transmissions in low-power cells (either downlink DL or uplink UL) are at the maximum power level which will in turn only further increase interference from macro cells since they too have to overcome higher interference from neighbors. As a result, users of the hotspot are connected to the surrounding macro cells, thereby further increasing the neighbor cell interference experienced by the low power cell.
From this discussion, it should be clear that it would be advantageous if the radio network control node (RNC) could be informed of the interference situation and take action, using e.g. admission or congestion control to reduce neighbor cell interference and to provide a better management of the hotspot traffic—in terms of air interface load.
A first problem is that there are no publicly available estimation methods known from prior art that allow an estimation of the neighbor cell interference after IS processing. A second problem is that there are no methods for estimation of the associated air-interface load after IS processing either. Thirdly, there are no means in the 3GPP standard for signaling of neighbor cell interference between the radio base station (RBS) and the RNC of the WCDMA system. Fourthly, there are no detailed algorithm known in prior art that are responsive to the load effect of neighbor cell interference, after IS processing, in the RNC. A fifth problem is that the only available neighbor cell interference management means is the relative grant and this mechanism is only available for cells in soft(er) handover with the user equipment (UE). On top of this, the relative grant can only provide a one-step grant reduction.
Consequently, there is a need for methods of enabling providing load measurements that take interference suppression into account, and to enable performing admission control based on the interference suppression affected load measurements.